When a diver is operating in the water, particularly near the surface, it is customary to have a marker such as a buoy or flag to indicate the presence of a diver to passing boats. A diver at or just below the surface is not easily visible and can be injured by a boat or its propeller, so marking is important. Some divers have tethered floats of flags but these markers are usually some distance away. A flag is mounted on a mast which projects above the surface when the diver is in a near horizontal position, face down for underwater observation. However, in some positions the flag is pulled under the surface unless constant adjustments are made. Also a fixed flag can become entangled in kelp or other obstructions and hinder or even trap a diver.
It is desirable to have a prominent marker which will project above the surface in any position of the diver and which will be easily deflected by obstacles without entangling the diver.